Rolling over, a milestone that typically occurs between 4 and 6 months, signifies the first time your baby is able to coordinate multiple muscles to achieve a common goal, says Kathryn Barnard, Ph.D., an infant mental health expert in Seattle. It's as if they realize, "Hey, this body of mine can move!" A primer:
Clues he's close: He's moving and shaking his arms and legs, and his head isn't as floppy. Both indicate your baby is gaining control over his muscles.
Direction matters: Rolling over is easier from belly to back, so give your baby plenty of tummy time when he's awake to practice. Left or right? Watch for which way your baby likes to roll; most babies have a preference, though one side isn't more common than the other.
How to help him: There's no need to rush this first achievement, but you can encourage your 4-month-old during playtime. When he's on his back, hold his hands and gently pull him up to strengthen core muscles. Or take both of his legs and roll him over from stomach to back and vice versa.